(a) Field of the Invention
The present invention relates to the production of gaseous nitrogen. It is more particularly concerned with satisfying moderate (typically 100 to 1000 Nm.sup.3 /h) and variable needs in nitrogen of high purity, i.e. typically containing less than 0.1% oxygen. In the present description, the flows under consideration are expressed in weight.
(b) Description of the Prior Art
High purity nitrogen is normally obtained by cryogenic means. For small consumptions, the construction of a self-contained known production unit represents a prohibitive investment, in the case of automated installations, and a more limited investment but with high labor expenses in the opposite case which always represents a high cost for the nitrogen produced.
A more economical solution consists in utilizing an evaporator, i.e. a container for liquid nitrogen with large capacity, for example many tens of thousands of liters, from which liquid nitrogen is withdrawn and vaporized. This solution is not very satisfactory from on an energy point of view, because the frigorific energy contained in liquid nitrogen is lost, and, in addition, it requires the presence, at a relatively small distance, of a unit for the production of liquid nitrogen, so that the cost of supplying the evaporator with a tank-truck remains moderate.